21G NITROGEN BODIES OF MODERN CHEMISTRY. 



oldest of the iiitrogeu compounds, the all prevailing bitter, picric acid. 

 This substance is of a pale-yellow color; by day a beautiful yellow, at 

 night white. Picric acid dyes animal tVibrics yellow, without the use of a 

 mordant ; it is almost poisonous, and particularly hostile to insects. It is 

 ])roved by experience that animal fabrics impregnated with picric acid, 

 T^■ith which we must always accept the yellow tint, are never attaclvcd 

 by moths or insects of any kind. When it is admissible, viz., wben the 

 color is not an objection and there is question merely of the preservation 

 of the material, the use of picric acid may be warmly recommended. It 

 is not so poisonous as to involve any danger in its use. Picric acid may 

 be fixed in vegetable fabrics when these are impregnated with a solu- 

 tion of caseine in borax. Still the acid can never be made perfectly fast 

 in these textures, while for animal fabrics it furnishes one of the most 

 durable of yellow dyes. This acid was formerly obtained from ditferent 

 substances— from indigo, for example. Common Bengal indigo, evap- 

 orated with nitric acid, leaves a deposit, which on the application of 

 heat decrepitates feebly. This is picric acid. 



Aloes, which is unfortunately in so common use as a drastic purga- 

 tive, digested with nitric acid also yields picric acid. 



Eecently the most abundant source of picric acid is gum acaroid, from 

 an Australian tree, {Xanthroehoca hastllis.) This resin, acted on by nitric 

 acid, affords the highest percentage of picric acid. I must mention one 

 more substance ; and this is obtained by the action of nitrogen IVom gly- 

 cerine, the so-called oleo-saccharum, a widely-ditfased article, which has 

 the formula : 



i\ U, H3 O3 



We may suppose it a three-fold water, in which three atoms of hydro- 

 gen are replaced by the bivalent radical glyceryl, 



o n5 



We can substitute nitryl for three atoms of the hydrogen in the 

 glycerine and then we have trinitroglycerine, glonoin, or glonoidin, the 

 Swedish explosive oil, a body first produced and examined by Sobrero, 

 and which is heavier than water, (LOG.) To prepare this we add a de- 

 ciliter of the purest glycerine, free from water, to Nordhausen sulphuric 

 acid and red fuming nitric acid, mixed in the proportions of G:4; 

 thus, c. g., one liter to GOO cubic centimeters and 400 cubic centimeters, 

 which mixture must be kept ice-cold ; it should stand in the cold several 

 hours. Then this liter is poured into at least ten liters of ice-cold water, 

 and the heavy, colorless oil, trinitroglycerine, sinks to the bottom ; it 

 should be well washed in water, in which it is nearly insoluble. In watery 

 alcohol it dissolves with difficulty, but readily in absolute alcohol, ether, 

 and pyroxylic spirit. It has a sweet but unpleasant taste, and induces 

 protracted headache, so that the hom<Popathists have seized upon it as 

 a specific against headache. This Swedish explosive oil is apparently 

 the most formidable of the nitrogen bodies 5 while one gram of gun- 



